For production of organic acids including succinic acid by fermentation, anaerobic bacteria such as those belonging to the genus Anaerobiospirillum and the genus Actinobacillus are usually used (Patent Documents 1 and 2, and Non-Patent Document 1). Use of anaerobic bacteria makes yields of products high, while demanding many nutrients for the proliferation of the anaerobic bacteria. Therefore, it is necessary to add a large amount of an organic nitrogen source such as corn steep liquor (CSL) in a medium. The abundant addition of the organic nitrogen source not only leads to an increase in cost of the medium but also leads to an increase in cost of purification for isolating the product, thereby resulting in being uneconomical.
In addition, a method in which aerobic bacteria such as coryneform bacteria are first cultured under an aerobic condition to proliferate the bacteria, and then, the bacteria are kept under anaerobic conditions as resting bacteria to produce an organic acid has also been known (Patent Documents 3 and 4). In this case, for proliferating bacterial cells, only a small amount of organic nitrogen is added, so this method is economical because the bacterial cells can grow sufficiently in a simple medium, but still to be improved in terms of the amount of produced organic acid of interest, the concentration thereof, and the production rate thereof per bacterial cell as well as simplification of the production method, and the like. In addition, fermentative production of an organic acid using a bacterium in which phosphoenolpyruvate carboxylase activity is enhanced has been reported (such as Patent Document 5), but further development of fermentative production for an organic acid has been demanded.
It has been reported that 2-oxoglutarate dehydrogenase (also called α-ketoglutarate dehydrogenase) activity was detected in a coryneform bacterium (Non-Patent Document 2), and the gene of 2-oxoglutarate dehydrogenase was cloned (Non-Patent Document 3). In addition, there is disclosed a production method for an amino acid using a microorganism in which 2-oxoglutarate dehydrogenase activity has been decreased (Patent Document 6).
However, producing an organic acid using a bacterium in which 2-oxoglutarate dehydrogenase activity is enhanced has not been reported so far.    Patent Document 1: U.S. Pat. No. 5,143,834    Patent Document 2: U.S. Pat. No. 5,504,004    Patent Document 3: JP-A-11-113588    Patent Document 4: JP-A-11-196888    Patent Document 5: JP-A-11-196887    Patent Document 6: WO 95/34672    Non-Patent Document 1: International Journal of Systematic Bacteriology (1999), 49, 207-216    Non-Patent Document 2: Shiio I, Ujigawa-Takeda K. 1980. Presence and regulation of α-ketoglutarate dehydrogenase complex in a glutamate-producing bacterium, Brevibacterium Flavum. Agric. Biol. Chem. 44: 1897-1904.    Non-Patent Document 3: Usuda Y, Tujimoto N, Abe C, Asakura Y, Kimura E, Kawahara Y, 0, Matsui H.1996. Molecular cloning of the Corynebacterium glutamicum (‘Brevibacterium lactofermentum’ AJ12036) odhA gene encoding a novel type of 2-oxoglutaratedehydrogenase. Microbiology. 142: 3347-54.